FEBRUARY1961 MONTHLY WEATHER REVIEW 45 DESCRIPTION OF THE 50-MB. PATTERNS OVER ANTARCTICA IN N. J. ROPAR 1 AND T. I. GRAY, JR.2 U.S. Weather Bureau, Washlngton, D.C. [Manuscript recelved June 24, 1960;revlsed November 25, 19601 ABSTRACT Seasonal variations in the 50-nlb. circulation over the Antarctic during 1058 are discussed and the features ob- served in 1957 are compared with those found in 1958. Both years exhibited similar patterns in the fall and winter seasons but differed somewhat in spring and summer. In 1957, the polar vortex of winter began to weaken in early Oct,ober and by November 21 a closed anticyclone at 50 mb. encompassed the continent. In 1958, the breakdown of the polar vortexmas more gradual and bythe end of Xovember the 50-mb. circulation was charactcrizcd by an irregu- lar pattern of closed cyclones and anticyclones rather than a dominant anticyclone. 1. INTRODUCTION 100-nleterint'ervuls and thcisotherms for every 5' Celsius. The nlapsincluded in this paperare excerpts Although it is too soon to receive the full amount of fro111 the series for t,he whole year which will be checked chec,ked dat'a from the Antarctic stations participating in and completed as the fi11wl data bec,ome arailablr. the IGY program, it is felt t'hat a sufficient number of' re- ports are available from t'he radio broadcast's in 1958 to 2. SUMMER 1957-1958 permit a preliminary analysis of t'he 50-mb. level over the continent (fig. 1). The 50-mb. chart, for January 15, 1958 (fig. a), is The present work is more or less a continuation of the fairlyrepresentat'ive of thesummer pattern at. the be- series of daily 50-mb. charts prepared by W. B. Moreland ginning of this year althoughthe circulation hadbeen of the US. Weather Bureau during his tourof duty as chief predominant81y anticyclonicfrom the middle to the end of of theAntarctic Weather Central at Little Americain December 1957. The flat contour gradient and relatively 1957. A comparison of t8hecircu1at)ion pat'terns for the two uniformtemperatures over the entire continent per- years reveals some significantdifferences in the spring and sisted until early Mnrch 1958. early summer seasons. A more detailed discussion of these The Low centered ut about 80' S., 100' E. apparently differences will be attempted later in this paper. hadmoved into t'his region fromthe west,ern coast of The series of charts for 1958 was plotted and analyzed Queen MaudLand. It' remainedover EastAntarctica at' IO-day intervals with data forone day on either side of but' exhibited a variable intensity and occasional break- the 10th day added as an aid in analysis. These charts oft' of secondar~-cells unt'il the middle of March, when a were basedon 0000 GMT data,although 1200 CMT data single pronouncedvort'ex and st,rong cyclonic circula- were used as an aid inanalysis. Extrapolations, by thick- tion developed over the whole continent. ness techniques, from levels between 100 mb. and 50 mb. The ridges along the coastal arms fluctuated in shape were carriedout whenever practicable to obt'ain better tmd extent, sometimes formingseparut'e small high coverage of the 50-inb. heightsand temperat'ures. This cells overthe continent. There appeared to be some method of analysis is similar to t'hat employed by Austin general westward drift to these ridges during t'he summer. and Krawitz [l] in their Northern Hemisphere st'udy, and The chart for February 5, 1958 (fig. 31, depicts the vari- byTeweles andFinger [2] intheir higher strnt'ospheric ationsin the syste~ns discussed above.The Low over analyses. t8hc Ross Seaseems to have been a part of t8helarger The area covered by the analysis is, of necessity, con- syst'errl cent'eredover East Antarctica. Rather prorni- fined tothe Antarctic Continent8 and adjacentmaters, nent ridges appeared over the coast near D'Urville and since 50-mb. dnta fromthe islands in the Southern over theEllswort~h Highland with the possibility of a Oceans arequite Ineager. The contours are drawn ut srnall closed Highin the lat't'er area at about 74' S., ____._ 85' W. It should be recognized, however, thattrying I Present affiliation: St. Louis University, St. Louis, Mo. to rnaint~aincontinuity of thesefact'ors onchart's 2 Present afElintioI1: International Antarctic Bnalysis Center, Central Burcau of hi(>- teorology, Melbourne, (?.I., Victorh, Australis. drawn for IO-day intervals may not be too satisfactory. Unauthenticated | Downloaded 09/25/21 08:01 AM UTC 3. AUTUMN 1958 the coast of theentire continent andtheband of highest winds (40 to 50 kt.)extended from h3irny to flit,tle Thetransition from sumnleris first'observed on the America. The center of t'hc circulation at about 85' S., chartfor hfarch 15, 1958 (fig. 4). The development of 40' W. llad :L tendency to drift about) the geographicpole this single prominent vort'ex appeared beto rather grdual. ina general west. to eastdirection but was mostoften The first area to indicate R strengthening of the cyclonic locatedbetween theSoutll Pole iLnd t'heWeddell Sew. circulation was the coastal region fromD'Urville to and betwwen the Yout'h Pole and the Pole of Relative Little America withwinds of 30 to 40 kt. reported at 1n;lccessibilit.y (82' S., 59' E.) during the year. stations in this part of t'he continent in t'he period March Thc large-scale features which developed by the middle 14-16. of April were retained without much change throughout By April 15 (fig. 5), the circulation was stronger over the fall season. Unauthenticated | Downloaded 09/25/21 08:01 AM UTC FEBRUARY1961 MONTHLY WEATHER REVIEW 47 FIGURE2.-50-mt) chart, January 11-16,1958. FIGURE4."50-mb. chart, AIarch 14-16, 1958. FIGURE3.-50-mb. chart, February 4-6, 1958. FIGITRE5.-50-mb. chart, April 14-16, 1958. Unauthenticated | Downloaded 09/25/21 08:01 AM UTC 48 MOKTHLY WEATHER R'EVIEW FEBRUARY1981 FIGURE6.-50-mb. chart, July 14-16, 1058. FIGURE8.-50 mb. chart, October 14-16, 1958. FIGURE7.-50-mb. chart, August 14-16, 1958. FIGURE0.-50-mb. chart,October 24-26, 1958. fact that the boundary of the polar night zone at 50 n!b. seasons indicate that four, and occcnsionally five, major was about 68' to 69' S. Unfortunately, no wind re- troughs were more common. ports for this level are available at comparable latit'udcs By t'hemiddle of July the temperatures over the in- on thePalmer Peninsula to check the validity of this terior were between -85O C. and - 90' C., while the tern- hypothesis. prratures over the coastal areas ranged from -81' C. at The three-wave pattern shown on this chart seems to the Belgian station, on the At'lantic side of the cont'inent, be arepresentative feature of themaps for July- and to -65' C. at,D'Urville, on the Pacific side.Again, it August 1958, whereas themaps for the spring and fall might be noted that while the isotherms did not exactly Unauthenticated | Downloaded 09/25/21 08:01 AM UTC FIGURE10.-50-mb. chart, November 4-6, 1958. FIGURE12.-50-mb. chart, November 27, 1958. parallel the contours t,here was only LL slight cross-contour 16th. on the 14th hIcllurdo reported a wind of 145 kt. orientation and, therefore,very little advective temper- at 50 mb. ature change in the winter months. Although the band of strong winds over t'he coasts of Thechart, for August 15, 1958 (fig. 7), shows rather the continent varied in intensityand lateral ext'ent during well-defined jet,s on opposite sides of the continent with the winter months, the winds over t'he coast of Wilkes winds of 50 t,o 60 kt,. over t,he coast of Queen Maud Land Imd and Vict'oria Land were rarely reported as less than andwinds over 100 kt. (at 67 mb.) at D'Urville on the 25 to 30 kt. at 50 mb. Unauthenticated | Downloaded 09/25/21 08:01 AM UTC 5. SPRING 1958 It is in the spring season that the most, radical changes take place inthe Antarctic stratospheric circulation. The rapid warming at very high levels in 1958, described by Hanson [3],was also not'iceable at 50 mb. and helped to produce the event'ual breakdown of the winter cyclone. The rate of warming at 50 mb. appcars to have been about the same at bot'h the coastal and interior stat,iorls inearly October and this act'ed tomaintain the band of highwinds encircling thecontinent from the coast of Queen Maud Land to Wilkes Land and the Ross Sea shown on the chart for October 15, 1958 (fig. 8). Winds of 80 kt. were reported at the Xorwegianst'ation, over 100 kt. at hlirny and D'Urville, and 100 kt. at Hallett, in the period October 14-16, 1958. It mightbe noted in passing that t'hc double center configuration of t'he polar vort'ex (fig. 8) was not a common occurrencealthough a similar pattern was evident on October 5, and once in each of May, June, and August'. On October 25, 1958(hg. 9),the center of thepolar vortex had shifted t'o about 75' S., 50' E. and a ridge had FIGURE14.-50-mb. chart, July 15, 1957. developed over the western Ross Sea and inland to near theSouth Pole. Theband of highwinds had moved inlandover Wilkes Land and the Ross Ice Shelf. The two features weakened gradually and appeared to move apparentwarm air advection and subsidence accom- panying this change in circulation caused a rise in tem, aroundthe cont'inent from west to east until a rather irregular pattern of isolatcd Lows and ridges was estab- peratureto -37' C.